1. Field of the Invention
This invention relates to an improvement to a flow control valve for controlling fluid such as gas passing through a conduit, and more particularly to a flow control valve which can smoothly open and close a valve body without being influenced by a primary pressure in the conduit.
2. Description of the Prior Art
FIG. 1 is a cross-sectional view of an example of a conventional electromagnetic valve described in Japanese Utility Model Publication No. 61-13819. In the drawing, a valve housing 1, forming a valve body, has a fluid inlet conduit 2 on the primary pressure side and a fluid outlet conduit 4 on the secondary pressure side connected to the conduit 4 through a valve aperture 3, both conduits separately formed in the valve housing.
A bulkhead through which the valve aperture 3 is formed is provided with a valve seat 3a and integrated, at a central portion thereof, with a valve support 5 which extends at a central portion of the bulkhead toward the inlet conduit 2.
The valve support 5 is provided on the upper surface thereof with a annular body 6 which is surrounded by an o-ring 7 over its outer peripheral surface.
The annular body 6 supports the inner surface of a cylindrical valve body 8 through the 0-ring 7, whereby a primary pressure chamber 9 is defined by the annular body 6 in an upper portion of the inside of the valve body 8. The primary pressure chamber 9 is connected to the inlet conduit 2 through a pressure introducing hole 10 and a strainer 11.
The inner diameter of the valve body 8 is selected to be equal to the effective valve diameter (d).
The valve body 8 is integrally coupled with a plunger 12 and urged by a spring 13 toward a direction in which the valve aperture 3 is closed.
A solenoid (electromagnetic coil) 14 is provided in the vicinity of the plunger 12 for opening and closing the valve body 8.
The operation of the above-mentioned control valve will be next explained. When the electromagnetic coil 14 is not energized, the valve body 8 is urged by the spring 13 to close the valve aperture 3. When the electromagnetic coil 14 is energized, the plunger 12 is lifted against the urging force of the spring 13, whereby the valve body is lifted with the plunger 12 to thereby open the valve aperture 3.
When the valve body 8 is closed, the primary pressure PI prevailing in the inlet conduit 2 acts on the whole outer surface of the valve body 8, while a portion of the primary pressure PI is introduced into the primary pressure chamber 9 through the strainer 11 and the pressure introducing hole 10.
Therefore, the valve body 8 receives a downwardly urging pressure P.sub.1d and an upwardly urging pressure P.sub.1s acting to open the valve in the primary pressure chamber 9 (S represents a pressure acting dimension in the valve body 8).
Since the inner diameter (D) of the cylindrical valve body 8 is equal to the effective valve diameter (d), the downwardly urging pressure P14 and the upwardly urging pressure P.sub.1s are equal so that they are cancelled by each other.
On the other hand, the bottom surface of the valve body 8 is urged by a secondary pressure P.sub.2 S on the secondary pressure side. However, since an upwardly urging force produced by the secondary pressure P.sub.2 S acts only on the bottom wall of the annular body 6, and not on the valve body 8, it may be ignored as a resistance preventing opening and closing action of the valve body 8.
Thus, even if the primary pressure P.sub.1 in the inlet conduit 2 is varied, the valve body is opened and closed, free from the influence caused by variations in the primary pressure P.sub.1.
FIG. 2 shows a cross-sectional view of a valve described in Japanese Utility Model Application No. 61-139415, previously filed by the same assignee of the present application.
A housing 15, defined in a valve chamber 1 connected with an output conduit 4, has therein a diaphragm piston 16 integrally coupled with the lower end of a plunger 12. Between the outer peripheral surface of the diaphragm piston 16 and the inner peripheral surface of the housing 15, there is arranged a flexible diaphragm 17 which expands and contracts in accordance with actions of the diaphragm piston 16.
Thus, a primary pressure introducing chamber 9 and a secondary pressure introducing chamber 15a are defined separately in the housing 15 with the flexible diaphragm 17 and the diaphragm 16.
The primary pressure introducing chamber 9 is connected to an inlet conduit 2 through a pressure introducing pipe 10, while the secondary pressure introducing chamber 15a is connected to the outlet conduit 4 through an through-hole 15b formed through a central portion of the bottom wall of the housing 15. The diaphragm piston 16 is integrally connected to the valve body 8 through a valve shaft 18 which penetrates the through-hole 15b.
The valve body 8, constructed as described above, is accommodated in the inlet conduit 2 in a manner such that it is upwardly urged by a spring 13. When the electromagnetic coil 14 is not energized, the valve body 8 is upwardly urged by the urging force of the spring 13 to close the valve opening 3. In this condition, the primary pressure P.sub.1 prevailing in the inlet conduit 2 is introduced though the pressure introducing pipe lo into the primary pressure introducing chamber 9, while the secondary pressure P.sub.2 in the outlet conduit 4 is introduced through the through-hole 15b into the secondary pressure introducing chamber 15a. At the same time, the primary pressure P.sub.1 acts on one surface of the valve body 8, and the secondary pressure P.sub.2 on the other surface of the same.
The primary and secondary pressures P.sub.1 and P.sub.2 are equal to those P.sub.1c and P.sub.sc in the primary and secondary pressure introducing chambers 9 and 5b, so that they are cancelled by each other.
Thus, even if pressures in the inlet and outlet conduits are varied, the valve body 8a will never be influenced by such variation, thereby ensuring smooth and precise opening and closing actions even with a small driving force.
However, in the electromagnetic valve shown in FIG. 1, the sliding portion includes the 0-ring 7 which may increase a sliding resistance and a starting resistance of the valve body 8, so that the driving force for the valve body 8 cannot be reduced.
Further, as the electromagnetic valve is used for a long period, the 0-ring 7 is first deteriorated due to abrasion, whereby a gas leak and further dangerous situations caused thereby will occur when the electromagnetic valve is employed to control a gas flow.
Also, since the electromagnetic valve of FIG. 1 is constructed such that the valve support 5 is projected from a central portion of the valve aperture toward the center of the valve body 8 and the annular body 6 is integrally formed on the upper end of the valve support 5, the valve support 5 has a quite low strength.
Moreover, the center of the valve support 5 must be precisely aligned with the center of the plunger 12. Such alignment requires a high machining accuracy, thereby rendering the production thereof difficult and the production cost increased.
The above-mentioned problems can be solved by the valve constructed as shown in FIG. 2. However, this type of valve also has a problem that, if the diaphragm is broken, a pressurized fluid in the primary side such as gas leaks to the secondary side, thereby damaging the security of the whole process.